possible, but not legal nor advisable. In the past those that did this were generally the rulers of countries which believed its royal family were gods. Since gods cannot be allowed to beget anything else but a god, then the logical choice was a sister or half-sister. Civilisations which did this included the Egyptians, and the Hawaiians. It is interesting to note however, that the royal families of these civilisations became so increasingly inbred that they had trouble producing viable heirs, which led to the downfall of dynasties. Which leads us to why it is neither legal nor wise to marry a sibling, even a half sibling. The genetic information for a sibling is very similar to your own. If there are predispositions towards certain weaknesses (eyesight, heart trouble, cancer) the blending of too close DNA can increase the likelihood of this happening. If there is the gene for cystic fibrosis (which requires both parents to have it for a child to inherit it), you more than double the chances of passing it to any child you have, if you marry a sibling. This inbreeding problem can be seen clearly in families such as Queen Victoria's. While she did not marry a sibling, she did marry a first cousin. Not illegal, and not too much of a problem, except that the family was already related many ways in the generations before that. In doing so, Victoria opened up a hornet's nest. A significant number of her male descendants in succeeding generations were haemophiliacs, and many of the females were carriers. A wider choice of brides in recent generations seems to have eliminated haemophilia in these lines. Society has almost universally frowned upon brother-sister marriage. It must have been known deep down that this was not a good thing healthwise. And many tribes rationalised it by saying that it was better to marry out, for dynastic alliance purposes. The moral: don't think of it.

idont think that thats good...

Yawl wanna marry yaw sista? WHY? The main reason would be that your genetic code is too close and you run the risk of hideously deformed kids